Objective To investigate the stress distribution of the femur after cemented prosthetic replacement in aged patients with comminuted intertrochanteric fracture and to analyze the difference of stress distribution between cemented long and short stem prosthesises.Methods A volunteer's left femur image data was obtained by spiral CT tomography.Then,the three-dimensional model of the femur was reconstructed with Mimics and Unigraphics modeling softwares.Based on the above analysis,we established three-dimensional modles of comminuted intertrochanteric fracture,long stem and short stem prothesises,and mantle layer of cement.Finally,we established the three-dimensional finite element model of these materials with software ABAQUS6.5,and carried out finite element analysis to the model in biomechanics.Results The stress disrilbution of the femur after cemented long and short stem prosthetic replacement didn't change significantly.The stress distribution of short stem between cement and prothetic stem were in the correlative area of distal end of the prothesis,and the lateral peak value was 21.3 MPa which exceeds the fatigue strength of bone cement;However,that of long stem were in the middle of medial interface and in the distal end of bilateral interface.There was no significant stress concentration zone in the mantle layer of cement which was used to reconstruct calcar femorale.Conclusion The stress distribution of the femur didn't change significantly after treating comminuted intertrochanteric fracture of aged patients with cemented long and short stem prosthesises.The cemented long stem prosthesises may be more suitable to treat these patients for its lower loosening probability.